1. Field of the Invention
The invention relates to a free wheel hub of a four wheel drive automobile which is able to change electrically between the two wheel driving condition and the four wheel driving condition.
2. Description of the Prior Art
In the prior art motor-driven free wheel hub system shown in FIG. 2, a spindle 2 is mounted on a drive shaft 1 to rotate uniformly, an axle hub 3 is mounted on the spindle 2 through bearings 4, 5. A hub body 6 and a hub cover 8 are fixed to the axle hub 3 by a bolt 7, and an electric motor 9 is mounted in the hub body 6. Between the drive shaft 1 and the axle hub 3, a commonly known free wheel hub mechanism comprising a motor gear 10, a handle gear 11, a handle 12, a cam follower 13, an outer clutch 14 and an inner clutch 15, are disposed. By the rotation of the electric motor, the motor gear 10 rotates the handle gear 11 on the handle 12. Thus, the cam follower 13 moves to the left side shown in FIG. 2 along a cam face 12a which is formed on the outer face of the handle 12 and engages with the cam follower 13. The cam follower 13 causes the outer clutch 14 to engage with the inner clutch 15 which is rotating with the drive shaft 1. Thereby the rotating torque of the drive shaft 1 is transmitted to the axle hub 3, and four wheel driving is achieved.
The current from the battery (not shown) to the electric motor 9 flows through a cord 16 which is wired through a hole 2A formed in the spindle 2. A pair of slip-rings 18 rest on an insulating member 21 which is seated on the outer face of a lock plate 17. The slip rings are electrically connected to the cord 16. The lock plate 17 is assembled to the spindle 2 through a lock nut 22 by a screw 23, with a pair of brushes 19 contacting the slip-rings 18. The brushes 19 are received in a brush case 20 which is assembled to the hub 3. The position of brush case 20 against the hub 3 is determined by means of the position of hub 3 between the bearings 4 and 5. Therefor, tightening the screw 23 by using a special tool (not shown) for assembling the brush case 20 to the hub 3 pre-loads the bearings 4 and 5. It is possible to break the brushes 19 with the special tool if the tool comes in contact with the brush. In order to insert lubricant between the bearings 4 and 5, an extremely careful adjustment requiring a lot of time is necessary or the brushes 19 will damaged.